1. Field of the Invention
The present invention relates to an apparatus, and a method for simultaneously establishing links with a plurality of nodes in a wireless network. The method can be implemented by a computer program which is stored in a computer readable medium.
2. Descriptions of the Related Art
With the rapid development of the computer network, various broadband services are now essential to the information industry. However, only part of computer users in the whole world can use high speed wired broadband services, such as the digital subscribe line (DSL) and the cable broadband access. From network telecommunication service providers' point of view, they desire to expand the coverage range of the broadband network. However, the related infrastructure costs for building the wired network make the providers move back. Broadband wireless techniques, hence, become an important solution. In light of communication distance, the current techniques of the wireless network can be classified into the wide area network (WAN), the metropolitan area network (MAN), the local area network (LAN), and the personal area network (PAN).
IEEE 802.16, worldwide interoperability for microwave access (WiMax), is a newly developing wireless transmission standard. The original establishing objective is to set up a radio standard of the metropolitan network to provide a wireless broadband connection technique of “the last mile” for the telecommunication industry. After continuously improved by the researchers of IEEE 802.16, more market requests can be supported now, such as various mobile and high speed broadband applications. Furthermore, comparing with IEEE 802.11, i.e., Wi-Fi and the third generation mobile communication (3G) technique, IEEE 802.16 has the advantages of larger network bandwidth, lower construction cost, better service quality, better expansibility, and extending the usage mode of a Wi-Fi hot spot.
IEEE 802.16 defines two operation modes. One is the point to multipoint (PMP) mode which is used in the aforementioned wireless broadband connection technique of “the last mile” to replace the conventional fixed network, such as the asymmetric digital subscriber line (ADSL) or the T1 subscriber line. The other operation mode is the mesh mode which provides a high speed and reliable backbone network. After several years' research on the PMP mode, the current techniques are very mature and already applied widely. Although the mesh mode has many advantages, it involves a more complicated technique and does not mature yet. Hence, the mesh mode still requires a lot of development.
As shown in FIG. 1, a conventional wireless network 1 operating under the mesh operation mode of IEEE 802.16 is disclosed. The wireless network 1 comprises a base station 101, a plurality of nodes 103, 105, . . . , 113 and an apparatus 115 which is about to join the wireless network 1. The base station 101 establishes the wireless network 1. The nodes 103, 105, . . . , 113 are various kinds of communication apparatuses for transmitting and routing data. The apparatus 115 has an effective connection range 100 which covers the nodes 107, 111, 113, and does not cover the nodes 103, 105, 109. That is, the nodes 107, 111, 113 can separately establish a link with the apparatus 115 for communication. When the apparatus 115 intends to join the wireless network 1, a network entry process is executed so that the apparatus 115 can join the wireless network 1 smoothly. After the network entry process is executed completely, the apparatus 115 logs into the base station 101. Next, the apparatus 115 performs a link establishment process to establish links between the apparatus 15 and the nodes 107, 111, 113 covered by the effective connection range 100. After the apparatus 15 establishes links with the nodes 107, 111, 113, the apparatus 115 can use resources and channels of the wireless network 1 to communicate with the neighboring nodes 107, 111, 113. In other words, the link must be established before data can be transmitted. When the apparatus 115, a starting node, separately establishes links with nodes 107, 111, 113, receiving nodes, there are three required steps to ensure the links to be established correctly. Messages transmitted in these three-step procedures all comprise Neighbor Link Establishment information elements (IEs). The Messages can be called Neighbor Link Establishment messages, which can be divided as a challenge message, a challenge response message, and an accept message.
Taking the link established between the apparatus 115 and the node 107 as an example, the apparatus 115 transmits a challenge message 102 to the node 107 first. After the node 107 receives the challenge message 102, an authentication procedure is performed to confirm that the node 107 is allowed to establish a link with the apparatus 115. After the authentication procedure is passed, the node 107 transmits a challenge response message 108 to the apparatus 115 to establish a unidirectional link from the node 107 to the apparatus 115. After the apparatus 115 receives the challenge response message 108, the authentication procedure is also performed to confirm that the apparatus 115 is allowed to establish a link with the node 107. After the authentication procedure is passed, the apparatus 115 transmits an accept message 114 to the node 107 to establish a unidirectional link from the apparatus 115 to the node 107.
Based on the current IEEE 802.16 standard, the apparatus 115 can only establish a bidirectional link with one node at a time. As shown in FIG. 1, after the apparatus 115 establishes the link with the node 107, the apparatus 115 can establish bidirectional links with the node 111 and the node 113 one by one based on the aforementioned three-step procedure. That is, the apparatus 115 separately transmits challenge messages 104, 106 to nodes 111, 113. The nodes 111, 113 separately transmit challenge response messages 110, 112 to the apparatus 115 to establish unidirectional links 119, 121. Finally, the apparatus 115 separately transmits accept messages 116, 118 to nodes 111, 113 to establish unidirectional links 125, 127.
Consequently, the apparatus 115 and nodes 107, 111, 113 can establish bidirectional links through the aforementioned series of link establishment operations. Then, the apparatus 115 can transmit data with the nodes 107, 111, 113 via the links. The aforementioned messages related to link establishment, such as the challenge messages 102, 104, 106, the challenge response messages 108, 110, 112, and the accept messages 114, 116, 118, are transmitted through mesh network configuration message (MSH-NCFG).
In IEEE 802.16 standard, a challenge message comprises a Neighbor Link Establishment information element with an action code field set to 0, a reserve field, and a neighborhood authentication value field. The challenge response message comprises a Neighbor Link Establishment information element with an action code field set to 1, a reserve field, a neighborhood authentication value field, and a Link ID. The accept message comprises a Neighbor Link Establishment information element with an action code field set to 2, a reserve field, and a Link ID.
Since the authentication procedure will not be performed after the accept messages 114, 116, 118 are transmitted, the accept messages 114, 116, 118 do not confirm the fields in the starting node and the receiving node. Such a process causes that the apparatus 115 only can establish a bidirectional link with one node at a time. That is, the apparatus 115 is allowed to establish the link with one of the nodes 111, 113 only when the bidirectional link with the node 107 is established. This causes that the link establishment process monopolizes resources. In other words, before the apparatus 115 completes the aforementioned three-step procedure for establishing the bidirectional link with one node, other nodes can not proceed to establish their links. If nodes establish links simultaneously, it is possible to cause a deadlock condition during the link establishing process among a group of nodes, and thus it is unable to build any links in the wireless network with the mesh mode.
If the apparatus 115 establishes links with the nodes 107, 111, 113 simultaneously, the nodes 107, 111, 113 can not distinguish that the link ID in the accept message is for which one of the nodes 107, 111, 113 because the accept message only comprises the link ID but does not comprise the neighborhood authentication value field. As a result, the apparatus 115 confuses the nodes 107, 111, 113, and the wireless network 1 operating in the mesh mode of IEEE 802.16 will collapse.
Since the apparatus 115 only can establish a link with one of nodes covered by the effective connection range 100 at a time, the time for establishing links with all nodes will be long, especially when the number of nodes covered by the effective connection range 100 increases. Furthermore, the link establishing process monopolizes resources. If nodes establish links simultaneously, the deadlock condition may occur. Consequently, how to make the apparatus 115 establish links with all nodes covered by the effective connection range 100 simultaneously to reduce the establishing time and to avoid the deadlock condition is still a problem for the industry to solve.